Removed the vector_owner interface.
Added some hash functions.
Replaced the unique std::vector<> with std::unordered_set<>.

 On branch master
 Changes to be committed:
	modified:   bin/Debug/schoolMarkLogger
	modified:   competence.hpp
	new file:   impl.hpp
	modified:   lesson.cpp
	modified:   lesson.hpp
	modified:   menu.hpp
	modified:   quartal.cpp
	modified:   quartal.hpp
	modified:   school_mark.hpp
	modified:   school_year.cpp
	modified:   school_year.hpp
	modified:   user.cpp
	modified:   user.hpp
	deleted:    vector_owner.hpp